The growing amounts of throw-away packaging, and, in general, the yearly increase in municipal waste have created a major public concern over how to effectively and safely dispose of such materials. It is well known that existing landfill facilities are becoming filled, and that new facilities are becoming even more difficult to acquire as the population grows and open spaces are being occupied with housing. Indeed, the rising expense of land acquisition and refuse disposal has become a major social problem which can only be curbed by the development of new means and methods of refuse disposal which avoid both direct incineration, which is very costly and frequently hazardous to community air quality, and landfill expansion.
Further, the collection of reclaimable fractions from municipal garbage provides an opportunity for communities involved with refuse collection to offset some of the cost associated with pickup and disposal operations by the subsequent sale of the reclaimed materials.
Of particular interest is a system for isolating and disposing plastic materials which are present in increasing amounts in a mixed refuse load. The burial of untreated plastic in landfills has proven to be an undesirable alternative because the irregularly shaped plastic parts create air voids which makes the fill difficult to compact. Even when comminuted or minced to reduce the particle size, such plastic wastes still have a great propensity to float if the landfill is subjected to water inundation thereby still reducing the effective capacity of the landfill to accept waste material.
The specific density of ferrous and non-ferrous metals, glass, miscellaneous dirt and fines and like materials allows these materials to be subject to preliminary separation, but cloth, cellulose articles, and like plastic materials still require special techniques to obtain their separation therefrom.
The use of thermoplastic polymeric materials which can be shaped or molded has become very popular for containers, packaging and even furniture. Such materials as polyethylene, polypropylene, polystyrene, polyvinyl chloride and the like are designated as thermoplastic because they soften when heated to between 230.degree. F. and 500.degree. F. and form a sticky surface enabling the plastic to adhere to a contact surface. Polyesters, phenolics, and the like are not thermoplastic and will not form a sticky adhesive surface when heated.
The final disposition of such plastic materials heretofore has been a landfill, an incinerator, and, in some instances, the materials have been isolated and thereafter recycled into other products. Most thermoplastic materials when incinerated will yield about 16,000 BTU per pound (excluding polyvinyl chloride which should never be incinerated because when it is combusted, it liberates free chlorine which dissolves in water to form hydrochloric acid) providing sufficient energy to fuel the incineration process. If polyvinyl chloride is included in the charge of materials subjected to the incineration process, the incinerator must be equipped to resist the corrosive nature of the chlorine derivatives as well as to wash the derivatives from the stack gases.
Landfill operations from heated plastics are easier and require less space as the plastics are "crinkled" and densified during the heating process which also makes size reduction for more efficient packing easier. The use of recovered thermoplastic wastes in the formation of new material is somewhat more difficult in that the contributing waste material must be of more or less constant composition. Completely charred plastics may be used as carbon particulates in the reinforcement of rubber products.
One prior art teaching, Fyfe et al (U.S. Pat. No. 3,599,788), relates to a method of removing waste thermoplastic materials from an assortment of waste materials being conveyed past a thermoplastic removal station. The method employs a rotatable cylinder contacting the material due to its own weight and either driven by the movement of the conveying means or in synchronism therewith from an independent power source. The cylinder has a surface of contact with the materials, and means provided to heat the cylinder to a temperature which softens the thermoplastic materials to a sufficient extent to enable the materials to adhere to the heated surface and be carried away from the conveying means. The softened and adhered thermoplastic material is thereafter removed from the cylinder with a scraper and directed to a collection point.
While Fyfe describes the broad idea of using a heated drum to segregate thermoplastics, the limited surface area of such a heated drum, considering the volume of waste flow, requires that it be heated to a very high temperature causing the drum to become glazed with sticky thermoplastic material. Furthermore, cellulosic materials and fine particulates adhere to the gummy drum surface and ultimately impair its function.
Thus a need exists for a scheme of waste segregation which will permit some species of waste to be incinerated, others to be transported to a landfill, and still others, recaptured and sold as reclaimed product. Accordingly, the present invention is directed to means and methods for segregating municipal garbage and trash into discrete fractions of ferrous metals, non-ferrous metals, glass, cloth, dirt and fines, thermoplastics and paper.